1. Field of the Invention
The present invention relates to a fuel supply apparatus for an internal combustion engine and, more particularly, to a fuel supply apparatus for supplying fuel to an internal combustion engine, comprising a fuel tank, a first fuel pump that supplies fuel from the fuel tank to a fuel line, a second fuel pump that supplies fuel from the fuel line via a pressurized line to at least one fuel valve that supplies fuel to the internal combustion engine at least indirectly and a fuel return line including a pressure regulator valve that connects the fuel line to the fuel tank.
2. Description of the Related Art
A fuel supply apparatus that supplies fuel by means of a first fuel pump from a fuel tank over a fuel line to a second fuel pump is known. The second fuel pump, for its part, supplies the fuel over a pressurized line to at least one fuel valve. Usually the number of the fuel valves is the same as the number of the cylinders in the internal combustion engine. The fuel supply apparatus can be constructed so that the fuel valves inject the fuel directly into the combustion chambers of the internal combustion engine. In operation of this fuel supply apparatus a higher pressure is required in the pressurized line leading to the fuel valves. After turning off the internal combustion engine it is desirable to mostly or entirely relieve the pressure in the fuel line and in the pressurized line to the internal combustion apparatus for safety reasons and because the fuel valves do not close entirely tightly.
The German disclosure document, DE 195 39 885 A1, describes a fuel supply apparatus, in which a valve device is provided for starting the internal combustion engine, so that the first fuel pump supplies the fuel with a high supply pressure to the fuel valves during the starting process. In many cases this high supply pressure is sufficient to start the internal combustion engine in the shortest possible time. Gas bubbles can be largely compressed in many cases between the first fuel pump and the second fuel pump by the elevated supply pressure so that a reliable operation of the internal combustion engine is guaranteed. In spite of that during the operation of the internal combustion engine at high temperatures and especially when the internal combustion engine is shut off at high temperatures, problems in both starting again and operation of the internal combustion engine occur at high temperatures. As has currently been established and described therein the gas bubbles of course are largely compressed at high pressure, however they are not sufficiently removed from the fuel supply apparatus. Furthermore it has currently been established that problems can occur at higher operating temperatures of the internal combustion engine because of the insufficient heat transfer from the fuel supply apparatus.
It is an object of the present invention to provide a fuel supply apparatus of the above-described kind that does not suffer from the above-described disadvantage.
This object and others, which will be made more apparent hereinafter, are attained in a fuel supply apparatus for supplying fuel to an internal combustion engine, comprising a fuel tank, a first fuel pump that supplies fuel from the fuel tank to a fuel line, a second fuel pump that supplies fuel from the fuel line via a pressurized line to at least one fuel valve so that the fuel at least indirectly reaches the internal combustion engine and a fuel return line including a pressure regulator valve that conducts fuel back from the fuel line to the fuel tank.
According to the invention a shut off valve is provided in the fuel return line hydraulically in series with the pressure regulator valve and a fuel scavenger line is provided that conducts the fuel back to the fuel tank, at least partially through the second fuel pump and through a hydraulic resistance.
Especially when there is a high thermal load on the fuel in the fuel supply apparatus, particularly when the second fuel pump is hot, also when the fuel is hot, the fuel supply apparatus according to the invention provides sufficient heat transfer from the fuel line so that no gas bubbles are generated in it. Fuel can be fed back to the fuel tank because of the scavenger line, which facilitates the advantageous heat transfer. Because of the closable shut off valve, fuel is returned over the scavenger line at high pressure in the fuel line between both fuel pumps, so that effective scavenging is guaranteed. Furthermore it is guaranteed that no gas bubbles or vapor bubbles occur at the inlet to the second fuel pump. Because of that feature a power loss, especially in the second fuel pump, and particularly at higher temperatures is reliably prevented. Reliable starting of the internal combustion engine is also guaranteed, especially at the higher temperatures.
Advantageous further embodiments of the invention are described and claimed in the appended dependent claims.